ls - list
lists non-hidden(non-dot) files in current directory.
options modify what is shown. 
arguments identify alternative directory files to list.
Both options and arguments are optional.


Options :
ls -a
lists all files in current directory, including 'hidden' (dot) files.
filenames starting with a . (dot) are not normally displayed by ls
dot files often used to store configuration options for various
  commands.

ls -l
long listing - shows file-type permissions, number of names, owner,
    time last modified, and name.

ls -d target
directory - surpresses traversal into subdirectories. Useful when
target is a directory, lists info about directory itself.

ls -q
quiet - shows unprintable characters as ?

ls -b
binary - shows unprintable characters as octal or symbolic

ls -F
classification flag  

/ at end if filename if directory
* at end if executable
@ at end if symbolic link 
Note - not part of file name
--color=auto - GNU? option similar to -F but using colors.


ls -R
recursive, (note Cap.) list all visible files 
    and contents of all sub-directories. Needs -a for all.


Several more available : man ls 

Arguments :
For ls, arguments are file names.

If name a non-directory file, lists just file.

If name directory, lists contents.

wild cards allow flexibility, close matches, but may give more than desired.


* - any
ls *
by itself - all visible in current and all next level directory contents
ls -d * - produces the same output as ls with no arguments.

ls r*
lists all files beginning with r

ls *s
lists all files ending with s

ls *s*
lists all files with s in its name including the filename s if it exists.

? - single character of any value

ls ???
lists all 3 character filenames.

ls f???
list all 4 character filenames where 1st character is f

ls [char-list]
ls [135] - each bracket represents possible alternative characters for
one character position. 

ls [a-f] - allows range specification. Range must be ascending ASCII.
ls [a-fn-z] - multiple ranges allowed.

[A-F][02468]  
   - This matches 2 characters in a row, 
     1st character A or B or C or D or E or F
     Note : comma is NOT used in not used in list.
     2nd character and even digit.

ls myfile[1-5]
lists mfile1, myfile2, ... myfile5 - if they exist.

ls [ab]file[1-5]
lists afile1 ... afile5, bfile1 ... bfile5  - if they exist.
 
[[:upper:]] - symbolic list reference. 
    the inner [:...:] is the list specifier.

Some available symbolic definitions. 
[:alnum:] - a-zA-Z0-9
[:alpha:] - a-zA-Z
[:digit:] - 0-9
[:lower:] - a-z
[:space:] - [tab],[space],[verttab],[formfeed],[carriage-return]
[:upper:] - A-Z
[:xdigit:] - 0-9a-fA-F


ls {string1,string2} 
    specifies list of alternative multi-character strings to match.
    strings may be of different lengths
    whole string matched.
    comma IS required as separator beteen strings in list.
  
ls f{1,13}
lists f1 and f13 if they exist. 



Wildcards will work with most commands that use a filename as a target,
so be very careful. It is possible to wipe out ALL of your files with
the wrong combination of options and wildcards.

Don't quote filename wildcards, they loose their definition. 

ls "*" 
  literally matches a file called * if it exists.

*Note - filename wildcards are not the same as regular expression wildcards.